1. Field of the Invention
The invention relates to decorative laminates. More particularly, the invention relates to a method for producing glossy decorative laminates, as well as controlling laminate gloss, using a cast polypropylene release sheet.
2. Description of the Prior Art
High pressure decorative laminates are currently manufactured with smooth glossy surfaces, textured surfaces, or deeply sculpted and embossed surfaces. As general background, decorative laminates prepared by heat and pressure consolidation have been produced commercially for a number of years, and have found widespread acceptance in the building and furniture industry as counter and tabletops, bathroom and kitchen work surfaces, wall paneling, flooring products, partitions and doors. These decorative laminates may be described as containing a number of laminae consolidated to form a unitary structure carrying a surface decoration. The surface decoration may range from something as simple as a solid color to something as complex as an embossed simulated wood grain finish.
Decorative laminates generally include plural layers of synthetic resin impregnated paper sheets bonded under heat and pressure to form a unitary structure. In normal practice, a decorative laminate sheet assembly, from the bottom up, includes a core of one or more phenolic resin impregnated sheets, above which lies a decorative melamine impregnated sheet. The decorative sheet may be further covered with a melamine impregnated overlay. The core, or base, functions to impart rigidity to the laminate and usually includes a solid substrate which may, or may not, be formed prior to the initial laminating steps. Prior to stacking, the sheets of the core member are impregnated with a water alcohol solution of phenol formaldehyde, dried and partially cured in a hot oven, and finally cut into shapes.
The core may, for example, include a plurality of sheets of 90-150 pound phenolic resin impregnated kraft paper and a substrate. The kraft paper is impregnated throughout and bonded with a substantially completely cured phenolic resin which has been converted to a thermoset state during the initial laminating step. The substrate may be a pre-cured plastic laminate, such as glass fiber-reinforced thermoset polyester resin laminates and the like, a wood product, such as hardboard, wood waste or particle boards, plywood and the like, a mineral base board, such as, cement-asbestos board, sheet rock, plaster board, and the like, or a combination of substrates.
The decorative sheet provides the laminate with an attractive appearance. The decorative sheet also dictates the surface characteristics of the decorative laminate. For example, the composition of the decorative sheet dictates the decorative laminate""s resistance to chemical agents, heat, light, shock and abrasion. Decorative sheets are commonly manufactured from high quality 50-125 ream weight, pigment filled, alpha cellulose paper impregnated with a water alcohol solution of melamine formaldehyde resin. The resin impregnated decorative sheets are subsequently dried, partially cured, and finally cut into sheets. The pigment filled, alpha cellulose paper of the decorative sheet, may include a solid color, a decorative design, or a photo-gravure reproduction of natural materials, such as, wood, marble, leather, etc. The aesthetic characteristics of the cellulose paper are revealed as the laminate""s decorative design upon completion of the decorative laminate.
Decorative laminates are generally manufactured by placing the resin impregnated core and decorative sheet between steel plates and subjecting the laminate stack to temperatures in the range of about 800-1600 psi for a time sufficient to consolidate the laminate and cure the resins (generally about 25 minutes to an hour). The pressure and heat force the resin in the paper sheets to flow, cure and consolidate the sheets into a unitary laminated mass referred to in the art as a decorative high pressure laminate. Finally, the formed decorative laminate is bonded to a reinforcing substrate, such as, plywood, hardboard, asbestos board, particle board or the like.
Generally, more than one laminate is formed at one time. Multiple laminates are formed by inserting a plurality of assembled sheets in a stack. Release sheets are positioned between the assembled sheets to separate the various laminates stacked together. After consolidation, the release sheets allow the individual laminates to be separated.
In recent years, textured decorative laminates have become very popular. The textured surfaces range from relatively shallow depressions, such as, textured (e.g., satin, matte or semigloss) surfaces, to relatively deeply sculpted or embossed surfaces having a noticeable three-dimensional effect, such as, wood grain, leather, slate, abstract patterns, creative designs etc. In instances where glossy textured decorative laminates are manufactured, very expensive techniques are currently required to ensure the desired texture and gloss are imparted to the decorative laminate.
While the physical characteristics, ease of manufacture, and expenses have long made polypropylene a desirable material for use as a release sheet in the production of decorative laminates, polypropylene release sheets have historically generated decorative laminates exhibiting limited gloss. For example, cast polypropylene release sheets have historically produced relatively dull decorative laminates exhibiting laminate gloss of less than six. Similarly, blown polypropylene release sheets generally only generate a gloss of around 10 to 12.
As such, a need exists for a method and apparatus for producing decorative laminates exhibiting excellent gloss characteristics. The present invention provides such a method and apparatus.
It is, therefore, an object of the present invention to provide a method for forming a glossy decorative laminate. The method is achieved by stacking a decorative laminate sheet assembly having a top layer, casting a polypropylene release sheet wherein the polypropylene release sheet is processed with chill rollers treated in a manner which improves the gloss characteristics of the resulting decorative laminate, positioning the polypropylene release sheet on the top layer of the decorative laminate sheet assembly, applying heat and pressure to the decorative laminate sheet assembly and the polypropylene release sheet sufficient to bond the decorative laminate and releasably bond the polypropylene release sheet to the top layer of the decorative laminate sheet assembly, and removing the polypropylene release sheet from the top layer of the decorative laminate sheet assembly to reveal a decorative laminate exhibiting desirable gloss characteristics.
It is also an object of the present invention to provide a decorative laminate lay-up including a decorative laminate sheet assembly having a top layer and a polypropylene release sheet applied to the top layer of the decorative laminate sheet assembly. The polypropylene release sheet is a cast polypropylene release sheet processed with chill rollers treated in a manner which improves the gloss characteristics of the resulting decorative laminate.
It is still a further object of the present invention to provide a decorative laminate manufactured in accordance with the process described above.